Name: message handler

Synonyms: message handler

Type: glossary

Description:
A <handler> you write that either <handle|handles> a <built-in message>
(such as <mouseUp>) or defines a <custom command>. Message handlers
begin with the <on> <control structure>.

References: on (control structure), handler (glossary),
custom command (glossary), handle (glossary), built-in message (glossary),
control structure (glossary), mouseUp (message)

